In situ formation and dispersion of lanthanide complexes in wormlike micelles.

Lanthanide-containing, water-based fluids normally suffer from low photoluminescent (PL) and/or colloidal stability, which greatly hinders their applications. Herein, we report the preparation of PL fluids which contain in situ formed europium complexes in aqueous solution. The strategy first relies on the construction of wormlike micelles by mixing a zwitterionic surfactant (tetradecyldimethylaminoxide, C 14 DMAO) and a tridentate ligand for a lanthanide cation (2,6-dipicolinic acid, DPA) in water. The addition of the dual-functionalized DPA to an aqueous solution of C 14 DMAO (100 mol L -1 ) induced non-monotonic rheological changes, with the expected formation of a pseudogemini surfactant at a DPA-to-C 14 DMAO molar ratio of approximately 1 : 2. When a third component of EuCl 3 is introduced to this system, complexes formed in situ between Eu 3+ and DPA, resulting in bright red-emission. Besides DPA, C 14 DMAO is also involved in the complexation, which squeezes out water molecules and greatly improves the PL stability of the fluid. The synergetic effect among Eu 3+ , DPA and C 14 DMAO leads to the high colloidal stability of the fluid, opening the door for a wide range of potential applications. Further tests indicate that this strategy can be easily expanded to other lanthanide cations such as Tb 3+ .